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// Copyright 2022 Datafuse Labs.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//     http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
use std::sync::Arc;

use crate::raw::*;

/// Layer is used to intercept the operations on the underlying storage.
///
/// Struct that implement this trait must accept input `Arc<dyn Accessor>` as inner,
/// and returns a new `Arc<dyn Accessor>` as output.
///
/// All functions in `Accessor` requires `&self`, so it's implementor's responsibility
/// to maintain the internal mutability. Please also keep in mind that `Accessor`
/// requires `Send` and `Sync`.
///
/// # Notes
///
/// ## Inner
///
/// It's required to implement `fn inner() -> Option<Arc<dyn Accessor>>` for layer's accessors.
///
/// By implement this method, all API calls will be forwarded to inner accessor instead.
///
/// # Examples
///
/// ```
/// use std::sync::Arc;
///
/// use opendal::raw::Accessor;
/// use opendal::Layer;
///
/// /// Implement the real accessor logic here.
/// #[derive(Debug)]
/// struct TraceAccessor {
///     inner: Arc<dyn Accessor>,
/// }
///
/// impl Accessor for TraceAccessor {}
///
/// /// The public struct that exposed to users.
/// ///
/// /// Will be used like `op.layer(TraceLayer)`
/// struct TraceLayer;
///
/// impl Layer for TraceLayer {
///     fn layer(&self, inner: Arc<dyn Accessor>) -> Arc<dyn Accessor> {
///         Arc::new(TraceAccessor { inner })
///     }
/// }
/// ```
pub trait Layer {
    /// Intercept the operations on the underlying storage.
    fn layer(&self, inner: Arc<dyn Accessor>) -> Arc<dyn Accessor>;
}

#[cfg(test)]
mod tests {
    use std::sync::Arc;

    use futures::lock::Mutex;

    use super::*;
    use crate::*;

    #[derive(Debug)]
    struct Test {
        #[allow(dead_code)]
        inner: Option<Arc<dyn Accessor>>,
        deleted: Arc<Mutex<bool>>,
    }

    impl Layer for &Test {
        fn layer(&self, inner: Arc<dyn Accessor>) -> Arc<dyn Accessor> {
            Arc::new(Test {
                inner: Some(inner.clone()),
                deleted: self.deleted.clone(),
            })
        }
    }

    #[async_trait::async_trait]
    impl Accessor for Test {
        async fn delete(&self, _: &str, _: OpDelete) -> Result<RpDelete> {
            let mut x = self.deleted.lock().await;
            *x = true;

            assert!(self.inner.is_some());

            // We will not call anything here to test the layer.
            Ok(RpDelete::default())
        }
    }

    #[tokio::test]
    async fn test_layer() {
        let test = Test {
            inner: None,
            deleted: Arc::new(Mutex::new(false)),
        };

        let op = Operator::from_env(Scheme::Fs).unwrap().layer(&test);

        op.object("xxxxx").delete().await.unwrap();

        assert!(*test.deleted.clone().lock().await);
    }
}